The microtip screens are characterized by an electronic field effect emission from an extended plane microtip cathode, a low consumption cold cathode, a rapid response time (1 .mu.s), a matrix addressing from the integrated tip-grid structure and a luminous emission by cathodoluminescence at a low/average voltage.
Known microtip screens are vacuum tubes generally constituted of two thin glass plates (approximately 1 mm), distanced by 200 .mu.m. The rigidity of the structure is ensured by spacers (balls of 200 .mu.m, for example) which enable the interelectrode distance to be maintained when the screen is placed under vacuum.
The front plate or anode plate is covered by a transparent conducting layer and luminophores.
The rear plate or cathode plate comprises a matrix network of field effect emitters deposited by thin film technology.
Each luminous dot (pixel) is associated with an oppositely located cathodic emitting surface and constituted of a large number of microtips (approximately 10,000 per mm.sup.2).
This emitting surface is defined by the intersection of a line (grid) and a column (cathodic conductor) of the matrix.
Subject to the introduction of a device for limiting the current in the tips, the large number of tips ensures a homogeneous emission between pixels (average effect) and eliminates the risks of local defects.
By virtue of the short tip-grid distance (.ltoreq.1 .mu.m) and the amplifying effect of the tip, a potential difference of less than 100 volts applied between line and column enables obtention, at the top of the tip, of an electric field greater than 10 to the power of 7 volts/cm, sufficient to cause the emission of electrons.
To fix the order of magnitude, a potential difference of 80 volts allows a current density of 1 mA/mm.sup.2 to be obtained. This value is sufficient in a screen of 1,000 lines, controlled sequentially line by line to obtain a high luminance (400 cd/m.sup.2) with a low voltage luminophore (400 volts) having a luminous yield of 3 lm/watt.
In light of the emission threshold (40-50 volts), the voltage which must be modulated on the columns to pass from the black level to the white level, is of the order of 30 to 40 volts.
The conventional structure of the cathode of a microtip screen especially comprises, deposited successively on a substrate of glass or silicon:
an insulation layer, PA1 a resistive layer of silicon or other material, PA1 "column conductors" constituted of a metallic layer which can be deposited either beneath or above the resistive layer, PA1 an insulating layer (Si or SiO2) which constitutes the grid insulator, PA1 a metallic layer which constitutes the grid.
After depositing the aforementioned layers, holes on which the microtips are then produced, are drilled into the grid and the grid insulators by known etching techniques.